Absorbent articles of the kind mentioned above, are known in a number of forms. Conventionally, the absorption core in such articles is produced by dry-defibration of cellulose pulp in the form of, for instance, rolls, bales or sheets and is converted in a fluffed form into a pulp web, sometimes with the admixture of so-called superabsorbents which are polymers having the ability to absorb several times their own weight of water or body fluid. The pulp core is often compressed, on the one hand to increase its fluid wicking capability and on the other hand to reduce the bulk of the absorbent core in order thereby to obtain an absorbent article which is as compact and demands as little space as possible.
In the technical field in question, it is common to use a vacuum pressure in order to deposit fibrous material onto a so-called forming wire, i.e. a kind of air permeable transport band, by supplying a mixture of air and absorption material to the wire wherein the air flows through the wire, thereby depositing its content of absorption core material onto said wire. Due to the fact that the layers of deposited material are air permeable per se, in this manner it is possible to deposit successive layers of material onto the forming wire, until the absorption core is formed.
U.S. Pat. No. 4,675,144 shows an apparatus for the formation of absorption cores, wherein a fibrous web is formed on an endless air-permeable band, a so called forming wire, as described above. Absorbent cores are then cut out from the formed fibrous web.
Further examples of apparatuses which employ the above mentioned technique are U.S. Pat. No. 4,739,910 and U.S. Pat. No. 4,690,853 which show a transport and folding device which utilise an air-permeable transport band, or a wire onto which absorption material is deposited, whereafter absorption cores are formed by means of a profiled, rotating brush.
When producing absorbent articles in accordance with the above mentioned method, it is usual to feed an air-permeable nonwoven material onto the forming wire such that the nonwoven material constitutes a carrier for the fibrous material which is deposited onto the forming wire. The nonwoven material, which may be elastic, will later constitute the sheet of material which is positioned closest to a wearer of the article. Further, in the technical field in question, it is known to use air-permeable, endless transport bands for pure transportation of different components, for instance between different manufacturing steps. One example of this is shown in U.S. Pat. No. 4,666,647.
A further example of a previously known technique is given in the Swedish patent application SE 9604803-8. This publication describes an apparatus for air-laying of a material in the form of fibres or granules onto an air-permeable, endless band wherein a second endless band is placed beneath the first band. The second endless band is designed with transverse bars which, on the one hand, define temporarily delimited spaces wherein vacuum exists, and on the other hand, provide a supporting force to the first endless band.
One problem with the use of all different types of air-permeable transport bands and forming wires is the relatively high friction which arises between the forming wire and the so called suction box. The suction box is the space, or spaces, at one of the surfaces of the forming wire, from where the evacuation of air takes place, whereby a vacuum pressure is created in the suction box. The suction box usually consists of a number of defining elements, such as wall elements and funnel-like evacuation elements. In addition, the suction box is delimited by the air-permeable endless band, i.e. the forming wire, which during operation is continuously moved past the suction box. Hereby, a certain amount of friction is created between the forming wire and its contact surfaces against the suction box, wherein the amount of friction depends, to a certain degree, on the size of the vacuum pressure which exists in the suction box. Neither is it unusual that small particles of absorption material which pass through the apertures in the air-permeable band are deposited onto the above-mentioned contact surfaces, whereby the friction is further increased.
The friction which arises, not only creates an increased energy consumption but also brings about an increase in temperature and a risk of operational problems due to an increased load on different components.
Furthermore, with the described type of equipment, it is necessary that the material which constitutes the transport band has a certain stiffness in order to counteract down-bending caused by the vacuum pressure which exists in the suction-box. This is normally solved by designing the transport band with a certain thickness and by placing a support plate, provided with a large number of holes, under the band which, accordingly, will slide on the plate. Another way is to substitute the support plate with supporting bars as in the above-mentioned Swedish patent application SE 9604803-8 which, however, requires a second endless band to carry the bars.